The Atari 5200 had a notoriously difficult to use joystick, which had analog aspects as well as a keypad. Press TAB to see the full layout of keys.
Press 1 for START. Use the ARROW KEYS to move and the CONTROL and ALT/OPTION keys for buttons 1 and 2. Use the NUMERIC KEYPAD for numbers 0-9, the ENTER ON THE NUMBER KEYPAD for the # key, and PLUS ON THE NUMBER KEYPAD for the * key.